This invention pertains to bearings for yo-yos. More particularly, it pertains to a double bearing, essentially two distinct bearings located side-by-side, positioned around the axle of a yo-yo to provide friction reduction and string centering that improves on the performance of a yo-yo with a single bearing.
Single bearings have been employed in yo-yos for approximately forty years and they dramatically reduce friction created between string and yo-yo parts during rapid spins of the yo-yo and during various tricks performed while the yo-yo is spinning. An early use of a ball bearing is taught by Isaacson in U.S. Pat. No. 3,175,326. A recent use of a roller bearing is taught by Marcantonio in U.S. Pat. No. 6,565,408 B1. Such single bearings are located at the midpoint of the axle around which the yo-yo spins between the string gap and the axle. Friction reduction allows the yo-yo to spin more rapidly and for a greater variety of tricks to be performed.
Although single bearings reduce friction, they still have several drawbacks. They are limited in terms of widths that are practically feasible and are available as stock items. Wide bearings can be important for avoiding friction between the string and the inner walls of the yo-yo and can also be important for performing advanced tricks. Also, single bearings used in yo-yos have bearing balls contained within two rings, an outer ring and an inner ring. A yo-yo string is wrapped around the outer ring of the bearing. In launching: a yo-yo, when the yo-yo reaches the bottom of a throw, the string abruptly pulls against the outer ring of the bearing, and introduces angular “tilting” or “wiggle” of the outer ring relative to the yo-yo's axle owing to clearances needed for individual bearing balls that must be free to roll around semi-circular internal grooves (referred to here as “tracks”) in the inner and outer rings that help contain the bearing balls between the rings. This wiggle or tilting of the outer bearing ring causes the string to slide off center and contact edges of yo-yo walls, thus imparting extra undesired friction that reduces spin time, and consequently reduces the time to perform tricks or to enjoy free-spinning suspension of yo-yo on the string. Wiggle of the outer bearing ring also gives rise to vibration and wiggle of the overall yo-yo.
Recently, improvements have been made in single bearing yo-yos. These include ceramic bearings with ceramic bearing balls, instead of the usual stainless steel bearing components, that reduce friction within the bearing itself1; curved outer rings that help keep the string centered, thus reducing friction with yo-yo walls such as the KonKave2 bearing; and different types of lubricants3 other than the previous standards such as grease or mineral oil. New lubricants such as light petroleum, synthetic oils, and Teflon-enriched oils are designed to reduce the internal yo-yo friction to extend spin times. However, in spite of these improvements, single bearing yo-yos are still subject to: angular tilting of the outer bearing ring; string friction with the walls of the yo-yo; and overall yo-yo vibration, wobbling, and “precession.” Precession refers to a well-known phenomena where the entire yo-yo tilts and twists during a spin as it slows down owing to forces of friction. As discussed by Watson4 precession is caused by frictional forces generated at various points within a yo-yo, including forces within a bearing (between the balls and track), and friction between the string and other moving parts of the yo-yo. The direction of the tilting or twisting depends on where the friction occurs relative to the axis of spin. The inertia and gyroscopic action of a fast spinning yo-yo resists precession, but as a yo-yo slows, the tilting and twisting become more pronounced. The effects of precession significantly shorten the useful duration of a spinning yo-yo.
The double bearing system disclosed here provides significant improvements over previous yo-yo bearing systems. The double bearing system, located between string and axle, provides two points of balance for the yo-yo instead of one. These two points of balance are located laterally outside the string position so that the string applies pressure to the bearing within the spacing between the two tracks of bearing balls. This position means the throwing force is distributed and balanced between two sets of bearing balls instead of being unstably balanced over a single track of bearing balls, and as a result there is a significant reduction in angular tilting of the outer ring for a double bearing as compared with a single bearing. Furthermore, the double bearing design significantly reduces precession effects for the yo-yo. Because the axle has two points of suspension instead of one, angular torque that typically causes precession has much less effect on a double bearing yo-yo. The result is much improved stability in vertical and horizontal orientation, meaning that there is less tilting and twisting.